PROPERTIES OF CORUNDUM-ZIRCONIA MATERIALS PREPARED
BY SELF-HEATING IN AN SHF ELECTROMAGNETIC FIELD
S. A. Suvorov,
I. A. Turkin,
and M. A. Dedovets
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp.2–5,June, 2003.
Engineering components made of high-temperature structural ceramics using traditional technologies may
show instability of properties because of the occurrence of imperfections, especially at the interphase boun
daries. Development of new techniques for the synthesis of high-melting oxide materials that would allow ef
fective control over the condition of the grain boundary phase in polycrystalline materials is at present an issue
of major concern.
The high-temperature synthesis of polycrystalline oxide
materials via controlled fusion/crystallization of eutectic
mixtures provides a route towards the structurally ordered
consolidation of crystalline phases and formation of materi-
als with a high fracture toughness .
Corundum materials, modified by the low-melting inter-
crystallite liquid phase of eutectic composition during the
high-temperature heating, exhibit a high resistance to static
and dynamic loadings but have a rather low temperature of
deformation onset .
A fusion – solidification process applied to the entire ob
ject provides a route to the synthesis of a thermally resistant
structure owing to the spatially-oriented crystallization; how
ever, the energy costs involved in the process are quite sig
The thermoelectric properties of imperfect dielectrics (to
which high-melting oxides belong) can be used to prepare
high-strength polycrystalline materials (including those of
eutectic composition) through controlling thermal effects
that arise from the interaction between individual constituent
components of the material and a microwave (MW) electro
Imperfect dielectrics such as silicon, aluminum, and
magnesium oxides and most of the silicate glasses are rather
modest MW absorbers at room temperature; however, their
absorption ability increases with temperature. Semiconduct
ing materials based on oxides of titanium, tin, copper, man
ganese, and others are capable of absorbing MW radiation
even at room temperature. The dielectric properties of
-based materials are strongly dependent on temperature:
when heated from 20 to 1000°C, their MW absorption ability
increases by 2 to 4 orders of magnitude. By combining the
proportion and distribution of radio-absorbing and ra-
dio-transparent phases in the structure of a material, one can
exert control over the intensity and dynamics of thermal ef-
fects in the bulk of a crystalline body exposed to a SHF elec-
tromagnetic field .
Microwaves, partly scattered off the surface and partly
penetrated into the bulk of the material, generate internal
electric fields that stimulate pulsation of ions and vibration
of polarized particles at a frequency proportional to the fre
quency of the electric field applied. The resistance to these
induced processes by the forces of inertia, elasticity, and
interparticle friction causes a transformation of the field en
ergy: the strength of the electric field decreases and the inten
sity of the thermal field increases, which results in the heat
ing of the material bulk.
The nonuniform reduction of the electromagnetic-field
strength over the volume of a polycrystalline body is closely
related to density fluctuations of the electrostatic field of
structural components and to physical and chemical pro
cesses involved in the heating of the material. Typically, the
phases of a material differ in their ability to absorb MW ener
gy and in the rate at which their electromagnetic parameters
change. This may result in the occurrence of local overheat
zones (hot spots) and finally lead to the effect of self-heating
of the specimen owing to the increase in conduction losses.
This behavior is a specific feature of imperfect dielectrics ex
posed to MW radiation .
Conventionally, three temperature levels can be dis
tinguished in materials showing a self-heating behavior
Refractories and Industrial Ceramics Vol. 44, No. 4, 2003
1083-4877/03/4404-0263$25.00 © 2003 Plenum Publishing Corporation
St. Petersburg State Technological Institute (Technical Univer
sity), St. Petersburg, Russia.